Future classes of advanced tactile missiles will require new ceramic materials for electromagnetic windows or radomes to meet stringent requirements arising from greater speeds and longer flight times. Such a ceramic material must have a high thermal stability, a low and thermally stable dielectric constant, a low coefficient of thermal expansion, resistance to high thermal shock, and resistance to erosion by rain.
Radome materials currently used are slip cast fused silica (SCFS) and Pyroceram 9606.TM. (2MgO.2Al.sub.2 O.sub.3.5SiO.sub.2, cordierite). While SCFS has excellent dielectric properties for radomes, the relatively low strength and rain erosion resistance of this material limits future application. Pyroceram 9606.TM. is more rain erosion resistant than SCFS, but is not as dielectrically stable with temperature.
Development of future electromagnetic window or radome materials is directed both toward improvement of the mechanical properties of SCFS and identification of new candidate ceramic materials. For example, materials in the system Si.sub.3 N.sub.4 --BN--SiO.sub.2 (Nitroxyceram) have the potential of being nearly as good as SCFC dielectrically and at least as good if not better than Pyroceram 9606.TM. in erosion resistance. However, this material requires expensive processing techniques such as hot isostatic pressing.
It would be desirable therefore to provide new ceramic materials for electromagnetic windows or radomes which possess the desired physical properties but which are relatively inexpensive to produce.